Electrical components of the type described above are known. Such components are produced from ceramic material having a positive temperature coefficient. The bases of such components are sheathed with a protective layer containing organic ingredients. Such components are generally used as PTC resistors. Donator-doped and acceptor-doped barium titanate, for example, may be used as the ceramic material of such a PTC resistor. The protective layer is usually a dried varnish applied to the base via a dip-varnishing method. The dried varnish typically contains organic solvents, such as xylene or acetol ester, and organic binders.
From reference DE 25 00 789 A1, electrical components are known which have a compressible intermediate layer, onto which a protective layer is applied. The intermediate layer absorbs tension forces that act on the base, which result from different thermal expansion coefficients of the base and the protective layer. The intermediate layer can include a material containing a solvent. The solvent in the material is evaporated by heating the material following applying the intermediate layer to the base.
From patent DE 51 956 C2, a PTC resistor is known that is surrounded by a housing, the material of which is free of nucleophiles. The housing is also encapsulated by a casting material. This configuration prevents a chemical reaction of the housing material with the base of the PTC resistor.
The quality of PTC resistors is based on their voltage storage stability, among other things. Voltage storage stability is indicative of an electrical voltage that a PTC resistor can withstand over an extended period of time, such as 24 hours, without losing its characteristic properties. Current flowing through a PTC resistor, resulting from applied voltage, heats the PTC resistor. Thus, the voltage storage stability of a PTC resistor is closely linked with its temperature stability. Since chemical processes with significant time constants play a role in the assessment of the stability of a PTC resistor, an electrical voltage applied only over a short period of time does not provide enough information for an assessment of the stability of a PTC resistor.
Known components have a disadvantage in that the varnish applied as a protective layer has a relatively high layer thickness, e.g., between 10 and 500 μm. This is due to the method of applying the varnish, namely the dip varnishing method. Encrusted surfaces form when the varnish dries, while a portion of organic ingredients is still present in the interior of the varnish. The encrusted surfaces prevent the organic ingredients from leaving the varnish during the drying process.
The protective layer of known components thus contains a residue of organic ingredients. These ingredients can reach the base, and can cause a chemical reaction. The chemical reaction can occur if the temperature of the component exceeds 220° C. as a result of a very high applied voltage. The reaction can depolarize grain borders of the ceramic. This destroys the PTC effect of the ceramic, causing the component to overheat if the voltage continues to be applied. Overheating can destroy the component. Therefore, known components have poor voltage storage stability.